Abstract:

This thesis presents a state-of-the-art review and brings new contributions to the waveform design for 5G systems in the presence of analog nonlinearities. A system model for the typical analog impairments at each stage of the transmitter and the receiver with a channel is first presented. The highlighted nonlinearities are power amplifier (PA), phase noise, and DC offset.

In this thesis, the further development of the orthogonal frequency division multiplexing (OFDM) is considered since the evolutionary approach from the 4G to the 5G is assumed to be more mature for technology demonstrations. In particular, the constant envelope OFDM (CE-OFDM) where phase modulation creates a constant envelope is studied, and the results indicate that CE-OFDM has an advantage compared to OFDM when the PA efficiency is taken into account in the simulations. Since the phase noise transforms just into an additive noise term after the phase detector, CE-OFDM is very resistant to phase noise unlike OFDM. CE-OFDM can be seen as an interesting candidate for the 5G scenarios when the power efficiency is a more important parameter than the spectral efficiency.

This thesis presents also new findings and results for the constant envelope tamed frequency modulation (TFM) and trellis-coded modulation (TCM) that is a traditional combined coding and modulation technique for spectral and power limited systems. In phase or frequency modulation spectral spreading and detection performance are controlled using a modulation index. In a simple analog implementation of TFM, the modulation index deviates during the transmission and generates time varying phase jitter.

In this work a modulation index estimator in conjunction with per-survivor processing (PSP) carrier phase estimation is presented for the TFM which has also very small spectral out-of-band radiation compared to other known CPM methods. A novel scheme based on multiple TCM, PSP and Reed–Solomon (RS) coding is proposed and shown to prevent the trellis-code to become a catastrophic code in the presence of phase noise. In general, the TCM and CPM modulations can complement the future adaptive OFDM based 5G systems.Väitöskirja sisältää kirjallisuuskatsauksen ja esittää uusia tuloksia tulevaisuuden 5G-järjestelmien aaltomuodon suunnitteluun analogiaosien aiheuttamien vääristymien läsnäollessa. Tyypillisille epälineaarisuuksille lähettimessä ja vastaanottimessa esitetään järjestelmämalli, joka sisältää myös kanavan. Erityistä huomiota kiinnitetään epälineaariseen tehovahvistimeen, vaihekohinaan ja DC offsetiin.